STATEN ISLAND, N.J. -- The son had mental health problems, and his father, fearing for the rest of the family’s safety, banished him to a small red tent in their Midland Beach backyard until he took his medication.

Early yesterday morning, those worst fears bore out, investigators believe, as Harold Delmar Jr., 46, fatally stabbed his 79-year-old father, then drove to southern New Jersey, where he ended his own life by setting himself and his car on fire.

The younger Delmar had locked the doors and chained himself to the driver’s seat, multiple law enforcement sources told the Advance.

The horrific chain of events began inside 1221 Mason Ave., where, at 3:52 a.m., police found the elder Delmar, stabbed several times in the neck and chest. He died of his wounds in Staten Island University Hospital, Ocean Breeze.

Investigators soon identified the victim’s son, an ex-Marine, as their prime suspect.

Staten Island Advance/Jan Somma-HammelRed tent in backyard of Mason Avenue home where Harold Delmar Jr. was alone with his demons.

"He was very unruly when he was not on his meds," said family friend Joe LaRocca. "The father was like tough love. He feared for his family. ... It goes to show what he was capable of."

Although authorities in New Jersey have not yet confirmed Harold Delmar Jr.’s identity, multiple police sources said the son drove more than 60 miles south, to the home of Nora Flanagan in Bayville, N.J.; the former Staten Islander had known Delmar in first grade.

"The last time she had seen him, which was well over a year ago, he was distraught, he was depressed, he had no job," a neighbor said.

Delmar pulled into the driveway, sources said, and, it’s believed, doused himself and his car with gasoline bought at a local BP station and set the fire. Both the body and the vehicle were charred beyond recognition, sources said.

Deputy Chief Michael Mohel, a spokesman for the Ocean County (N.J.) prosecutor’s office, said two patrol officers came across a Chevy Aveo "engulfed in flames" in a driveway on Station Road in Bayville about 6:05 a.m.

After firefighters doused the blaze, they found the badly burned body of a man in the driver’s seat. Mohel would not speculate on the identity until an autopsy has been completed, though NYPD and law enforcement sources say investigators believe the body is that of Delmar Jr.

The cause remains under investigation but the manner of death was "dermal injuries and smoke inhalation," Mohel said.

LaRocca, who owns the nearby LaRocca’s Italian Ices and Pizzeria, has known the Delmar family for years, and got along well with the elder Delmar’s son Robert, who worked in the restaurant.

"Good people — I’d feel proud to call them my family," LaRocca said.

Delmar Sr., a retiree who lived with his adult children and took care of his sick wife, was regularly seen in the area, walking out to Lincoln Avenue and Hylan Boulevard to shop and do chores.

"The father was a loving soul," LaRocca said. "He’d walk everywhere he needed to go. ... He got his shopping cart and he was off running."

LaRocca added, "This is a shock, a shock to the community."

Members of the Delmar family gathered beyond the yellow crime scene tape that blocked off Mason Avenue, as neighbors greeted and consoled them.

"He was a good man and that’s all I can tell you. A family man," said a woman who identified herself as his daughter but declined to give her name. Delmar Sr. was a regular at the New Dorp Beach Friendship Club, she said.

Other family members declined comment.

"His granddaughter just got married recently," said neighbor Angie Amaniera. "He was a great guy."

Ms. Amaniera said she was "shocked" by the killing, and the information that the son was the police’s prime suspect. Still, she said, the rest of the family seemed less surprised that Delmar Jr. was capable of such violence.

"I think he threatened somebody recently," she said.

One man, who lives down the block from the Delmars but refused to give his name, said the younger Delmar had trouble living with other family members, and had at one point been living in a car before moving into the tent.

"Every day, he would walk down the beach with his fishing rod," the neighbor said.

Advance records show that Harold Delmar Jr. graduated from McKee High School in 1982, and joined the U.S. Marine Corps in January 1985. He was promoted to private first class later that year, while serving at the Marine Corps Ground Combat Center in Twentynine Palms, Calif.